Liquid metal pouring duct, process and device for homogenizing metal

ABSTRACT

A liquid metal casting conduit (1) is shaped as a partial torus and has an inductor (3) embedded in concrete and whose turns are asymmetrical with respect to the axes (XX&#39;) and (YY&#39;) of the conduit. It is used for to the homogenization of the metal temperature when the conduit is secured to a low pressure casting ladle (7).

BACKGROUND OF THE INVENTION

The present invention concerns pouring liquid metal in order tomanufacture objects from steels, superalloys and other ferrous ornon-ferrous metal alloys.

The invention relates, in the first place, to a pouring ductincorporating a closed cross section opening, at one end, into a pouringorifice in order to feed at least one mold, and of the type comprising,along its length, at least one heating element composed of an inductionthrough whose cooled turns an alternating electric current (˜, U,F)flows. The coil is embedded in concrete surrounding a heat-resistanttube (see, for example, U.S. Pat. No. 5,708,257 in the Applicant'sname). This duct proves especially advantageous for pouring metalshaving high melting points.

This heating duct eliminates the danger of cooling and solidification ofa metal alloy having a pouring temperature of at least 1,400° C. betweentwo successive pouring operations.

Furthermore, this duct configuration yields a number of advantages overthe conventional state of the art, these advantages being described, forexample, in U.S. Pat. No. 4,475,721 in the name of Pont-a-Mousson SA andrelating to the simplicity of manufacture of the duct (see U.S. Pat. No.5,708,257 in the Applicant's name).

However, a number of heterogeneous temperature phenomena can be observedin this type of duct, which become more pronounced when the duct isrounded. As a consequence, metal-filling and -solidification differencesoccur in the casting mold.

SUMMARY OF THE INVENTION

This invention is intended to solve these problems. In particular, thehomogeneous temperature of the metal ensures the uniformity of theconditions for filling and solidification of complex or multipleimpressions in a casting mold, thereby making it possible to strictlycontrol the defect rates (shrink cavities, cracks, etc.) found on theobjects. The duct according to the invention gives such results becauseof asymmetrical induction coil turns. To make uniform the longitudinaltemperature variation of the metal, the turns in the inductor areshifted and the density thereof increases at the end of the pouringorifice designed for feeding the mold.

To make uniform the transverse variations of the metal temperature, theinductor turns form a spiral which is offset, in relation to the duct,toward the axis of rotation of the covering torus of this duct.

In accordance with other variants:

the turns of the inductor are circular in shape, or

the turns of the inductor have an elliptical shape.

The invention also concerns a process intended to yield the sameresults. This process for achieving homogenization of the temperature ofa metal circulating in a duct in the shape of a partial torus of thetype described above is characterized by the fact that an electriccurrent having a frequency of less than 15,000 Hz is fed to theinductor.

The invention also concerns a low-pressure metal pouring unit comprisinga foundry ladle incorporating a pressurized gas source which opens intothe upper part of the ladle and a metal-outlet orifice, this unit beingcharacterized by the fact that the outlet orifice empties into a ductconforming to the duct described above.

BRIEF DESCRIPTION OF THE FIGURES

One embodiment of the invention will now be described with reference tothe attached drawings, in which:

FIG. 1 is a vertical cross-section of a heated pouring duct according tothe invention.

FIG. 2 is a vertical cross-section of a reduced-pressure metal pouringunit comprising a duct of the type described in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The apparatus shown in FIG. 1 is a duct 1 having a closed cross-sectionwhich opens at one end through an orifice 2 and comprises, over thelength thereof, a heating element constituted by a coil-shaped inductor3 through whose cooled turns 4 an alternating electric current (-, U,F)travels. This inductor 3 is embedded in concrete 5 surrounding aheat-resistant tube 6. The turns 4 are asymmetrical in relation to theaxes of symmetry of the duct X--X' and Y--Y'. The duct is shaped like apartial torus, the axis of rotation of which passes through a point C.The axis X--X' corresponds to the axis of the duct. The axis Y--Y'corresponds to the radius of curvature passing through point C and is inthe median position with respect to the two ends of the duct. Thedensity of the turns 4 is greater at the end portion incorporating thepouring orifice 2, since these turns are closer together on this side ofthe axis Y--Y'. The inductor is shaped like a spiral, whose axis Z--Z'is closer to point C than is the axis X--X', with the result that thecoil turns are shifted toward the inside of the concavity of the duct.

The unit illustrated in FIG. 2 is a pouring apparatus comprising a ladle7 to which the duct 1 is fastened by a clamping device 8 known inaccordance with the state of the art. The ladle and duct hold liquidmetal 9, which is supplied through a lateral filling door 10. The ladleincorporates a graphite rod 11 which is heated to high temperature andradiates on the metal surface.

The upper part of the ladle comprises a duct 12, which feeds apressurized gas flow into the ladle above the molten metal bath.

A pressure-control apparatus 13 mounted on the duct 12 comprises apressure-measuring device and a valve. A block 14 positioned beneath theduct 1 makes it possible to set the pouring position. The ladle can beinclined by rotation on a system of rollers 15 and 16. The low-pressurepouring unit works in the following way: The ladle is filled with metal9. A mold (not shown) is brought into contact with the outlet orifice 2.The mold is filled by applying the pressure of the gas issuing from theduct 12 to the surface of the metal. Several molds are filled insuccession. The pouring duct 1 keeps the temperature of the metalhomogeneous during and between each mold-filling operation, using theinductor fed with alternating current.

Following the multiple-mold pouring cycle, the metal remaining at thebottom of the ladle is drained away through the filling door 10 byrotation on the rollers 15 and 16.

We claim:
 1. An elongate duct (1) for pouring liquid metal to feed acasting mold, the duct having a closed cross-section opening at one,exit end to define a pouring orifice (2) for feeding said mold, saidduct comprising, over its length, a heating element constituted by acoil-shaped inductor (3) through whose cooled turns (4) an alternatingelectric current flows, said inductor being embedded in concrete (5)surrounding a heat-resistant tube (6), wherein the inductor turns as awhole are asymmetrically disposed in both a longitudinal direction ofthe duct, being more closely spaced proximate said exit end, and in atransverse direction of the duct such that a longitudinal axis of theinductor turns is laterally offset from a longitudinal axis of the duct,so as to make the temperature of the metal (9) homogeneous.
 2. A ductaccording to claim 1, wherein the density of the turns increases as theyapproach the pouring orifice.
 3. A duct according to claim 1 in the formof a partial torus, wherein the inductor (3) forms a spiral having alongitudinal axis (Z, Z') positioned closer to the axis of rotation ofthe torus than the longitudinal axis (X--X') of the duct.
 4. A ductaccording to claim 1, wherein the individual turns of the inductor arecircular in shape.
 5. A duct according to claim 1, wherein theindividual turns of the inductor have an elliptical shape.
 6. A ductaccording to claim 3, wherein said partial torus has a constant radiusof curvature.